Ultrasound-guided hydrorelease/hydrodissection reduces gliding resistance in a rat sciatic nerve adhesion model : a preclinical experimental study

BACKGROUND: Ultrasound-guided nerve hydrodissection (HD), often referred to as hydrorelease (HR) in Asia, is increasingly used for peripheral nerve entrapment. Although HD/HR is clinically applied to separate nerves from surrounding tissues and potentially improve symptoms, its mechanical effects on nerve mobility under perineural adhesions remain incompletely understood. This study aimed to establish a mild rat sciatic nerve adhesion model and to evaluate whether ultrasound-guided HR/HD improves nerve gliding without impairing nerve function. METHODS: A rat sciatic nerve adhesion model was created in the right thigh by exposing the sciatic nerve, coagulating the nerve bed, and fixing both ends of the nerve to the bed with 8 - 0 nylon sutures; the contralateral side served as control. Adhesion severity was assessed macroscopically at 1, 3, and 6 weeks (stage 0-2) by two examiners, and tensile strength required to detach the nerve from the bed was measured using a digital force gauge. Nerve function at 6 weeks was evaluated by nerve conduction studies (CMAP and motor nerve conduction velocity). Based on model characterization, ultrasound-guided HR/HD was performed at 6 weeks using 2 mL saline to circumferentially dissect the paraneural sheath, and gross adhesion and tensile strength were reassessed one day after injection. Statistical analyses included one-way ANOVA, Tukey's test, and Kendall's coefficient of concordance. RESULTS: Adhesions progressed over time, with most nerves showing stage 2 adhesions at 6 weeks; inter-observer agreement was high (Kendall's coefficient 0.92). Tensile strength increased with time (0.91 ± 0.11 N in controls; 1.12 ± 0.29 N at 1 week; 1.72 ± 0.58 N at 3 weeks; 3.10 ± 0.18 N at 6 weeks), with significantly higher values at 3 and 6 weeks compared with earlier time points (P < 0.05). Motor nerve conduction parameters at 6 weeks did not differ significantly between adhesion and control sides. Ultrasound-guided HR/HD significantly reduced tensile strength in the adhesion model (2.05 ± 0.16 N; P < 0.05 vs. untreated adhesions), although values remained higher than controls. CONCLUSIONS: In a rat sciatic nerve adhesion model with preserved nerve conduction, ultrasound-guided HR/HD reduced tensile strength required to detach the nerve from the bed, indicating improved mechanical mobility/gliding under adhesions. These findings support HR/HD as a minimally invasive approach to enhance nerve gliding in mild perineural adhesion conditions and warrant further studies on long-term outcomes and imaging-pathology correlations.